Reverse pulse generator



Sept. 6, 1960 D. T. DICKSON ETAL 2,951,978

REVERSE PULSE GENERATOR Filed May 29, 1957 2 Sheets-Sheet l FIG. l

+ ll INVENTORSJ DAVID T. DICKSON 8| JOHN W. VAN DYKE BY w/W ATTORNEYSept. 6, 1960 D. T. DICKSON ETAL 2,951,978

REVERSE PULSE GENERATOR Filed May 29, 195'] 2 Sheets-Sheet 2 FORWARDVOLTAGE VOLTAGE O l REVERSE I VOLTAGE I I I I FORWARD REVERSE FIG. 2

INVENTOR DAVID T. DICKSON 8 JOHN W. VAN DYKE ATTORNEY Patented Sept. 6,1960 2,951,978 REVERSE PULSE GENERATOR David Thomas Dickson, Burton, andJohn W. Van Dyke, Seattle, Wash., assignors, by mesne' assignments, toThor P. Ulvestad and David T. Dickson Filed May 29, 1957, Ser. No.662,474 21 Claims. (Cl. 322.6)

The present invention relates to the rapid reversal of electricalcurrent direction with the substantial elimination of any off periodbetween the diiferently directed unidirectional pulses of electricalcurrent. The present invention is particularly directed to electrolyticprocesses and especially electroplating by a procedure in which thecurrent direction is rapidly reversed and the off period substantiallyeliminated so that the ions in the area surrounding the cathodeelectrode can be more efficiently replenished and the electrolyticprocess enhanced as a result of the fact that the ions are moreefiiciently replenished in the area of the cathode and the anode is moreefliciently depolarized.

In accordance with the invention, an electrical current is supplied froma DO generator and the current direction is rapidly reversed with thesubstantial elimination of any off period between the forward andreverse current directions. It has been found that this rapid reversalof current direction aids in replenishing the ions in the area aroundthe cathode and that the anodes are more efliciently depolarized. As aresult, the invention enables a greater current density to be used inboth directions and the electrolytic process proceeds more rapidly andmore uniformly.

Referring more particularly to the process of electroplating, there areseveral important factors governing the value and usefulness of anelectroplating process. These are (1) electrical efficiency, (2) speed,(3) quality of finish and (4) the amount of prior and subsequenttreatment such as bufiing and polishing which are necessary inconnection with the process. The factor of speed is of particularimportance since if the time of treatment can be shortened by 50% to75%, a decrease in electroplating efliciency can be tolerated. Further,if the strength and uniformity and also the quality of the finish(smoothness and brightness) can be enhanced, such improvement willjustify a lowered electrical efficiency.

In the past, some advantage has been attained by the utilization ofreverse current plating. In this method, a generator was used for acurrent source and the field was reversed periodically by means of amechanical switch. Some small improvement in plating was obtained byreverse current plating. However, the time constant of the field madeswitching relatively slow. Attempts were made to improve the situationby the use of rectifier power supplies but it was still necessary toswitch the primary circuit off, to reverse the output of the rectifierand to turn on the primary, all mechanically.

In accordance with the present invention, the direction of theelectrical current is reversed electronically and at a much more rapidrate so that the off period between forward and reverse is substantiallyeliminated and the electrolytic process improved in themanner previouslyindicated.

In accordance with the present invention a general improvement has beenmade in electrolytic processes. Thus, in addition to improvement in theelectroplating process, electrolytic cleaning or polishing and theanodizing of metals, e.g. aluminum and magnesium, are also improved. Theinvention is also applicable throughout the electrochemical industry,and may be utilized to advantage in electrolytic decompositions.

In accordance with the present invention, the reverse current produces acleaning or etching effect and the deposit is free from impuritiesbetween the various layers of plate, whereas in the mechanical switchingmethod, the deposit is subject to laminations and will break up inductility tests.

The invention will now be more fully described in connection with theaccompanying drawings in which:

Fig. 1 is a circuit diagram illustrating the applicability of theinvention to an electrolytic process such as electroplating; and,

Fig. 2 is a graph comparing voltage with time for the purpose ofillustrating a single cycle of output current.

Referring more particularly to the drawings, a direct current generator10 is fitted with two identical sets of field coils 11 and 12 and withcommutating interpoles 13 and 14. One terminal of one set of field coils11 is connected to the anode of an arc-type gas valve or thyratron 15,the anode being identified by the numerals 16. In place of the thyratron15, any other type of control such as an ignitron may be employed. Theother end of the same set of coils 11 is connected to an adjustableresistor bank 17. The resistor bank 17 is in turn connected with thepositive terminal of a suitable source of direct current.

The second set of field coils 12 is similarly connected to an arc-typegas valve 18 and particularly to the anode 19 thereof. Field coils 12are also connected to an adjustable bank of resistors 20, said resistorbank 20 being in turn connected with the positive terminal of the directcurrent source.

The field coils 11 and 12 are oppositely wound so that, when directcurrent is flowing through coil 11, the armature polarity will be suchthat the terminal connected to the anode 21 of the electroplating bath22 will be positive while the terminal connected to the cathode 23 ofthe electroplating bath 22 will be negative.

When the field coil 12 is energized, the above set forth polarity willbe reversed, and the anode 21 will be negative while the cathode 23 willbe positive.

A capacitor 24 is connected between the anodes 16 and 19 of the arc-typegas valves 15 and 18. The anode 25 of a third arc-type gas valve 26 issimilarly connected through capacitors 27 and 28 to the anodes 16 and 19respectively of the valves 15 and 18.

The anode 25 of the valve 26 is connected to the positive terminal ofthe direct current supply through resistors 29 and the inductor 30 (theinductor 30 being not essential).

The cathode returns of the valves 15, 18 and 26 are common and connectto the negative terminal of the direct current supply. The grids of thevalves 15, 18 and 26 are suitably biased and controlled by a separatecon troller 31 which provides spaced trigger pulses for the valves orthyratrons 15, 18 and 26.

The sequence of operation is as follows: A trigger pulse from thecontroller 31 causes the valve 15 to conduct, and current builds up infield coil 11 which produces a magnetic field in the armature orinterpole 14. Current is therefore induced in the armature winding andits associated circuit causing metal from the plating bath 22 to bedeposited on the cathode 23. After a short interval, determined by thecontrol element 32 of control 31, a second pulse is applied, this secondpulse being directed to the grid of valve 18 causing the valve 18 toconduct. The drop in voltage at the anode of valve 18 lowers thepotential of the anode 16 of valve 15 and extinguishes the arc therein.The current is thus cut off in the field coil 11 and is built up in thefield coil 12. The polarity of the armature is thus rapidly reversed andthe anode 16 becomes temporarily cathodic while the cathode 33 of thevalve 15 becomes temporarily anodic. The time and voltage relationswhich can be employed in accordance with the invention are discussedhereinafter.

After an interval determined by the control element 34 of the controller31, a pulse fires valve 26 which extinguishes the arc in valve 18 thuscausing the current and voltage of the generator to drop to zero. Afteran interval determined by control element 35 of the controller 31, apulse fires valve 15 and the cycle repeats.

As will be understood, the time intervals for each pulse are separatelyadjustable and the voltage and amperage of the forward pulse areadjustable by means of the resistor 17 while'the voltage and amperage ofthe reverse pulse are controlled by the resistor 20. In this manner, thestrength and timing of each pulse can be individually determined.

For example, the pulse interval may be set to 0.7 second with a forwardinterval of 0.4 second and a reverse interval of 0.1 second. The forwardvoltage may be 30 volts and the reverse voltage 45 volts. At thesesettings, a 2-2.5 mil coating of nickel may be plated from a Watts-typenickel bath in 10 minutes. The finish achieved is superior to thatproduced by standard methods both in grain and brightness and thespeed-of-deposition is far in excess of that which is normally achieved.These superior results are due to the rapid reversal, the short cycle,and the rest period which permit a much greater current density than anyprevious method. The short high-current reverse pulse produces superiordepolarization in certain cases which permits the achievement of heavierdeposits of the metal which is plated.

The cycle of output current in accordance with the invention isgraphically represented in Fig. 2 where voltageis correlated with time.Fig. 2 is self-explanatory and shows a complete cycle including theforward pulse, the reverse pulse and the ofi period. The rapid reversalof current direction between the forward and reverse pulses and the useof a rest period provides superior depolarization and permits thereplenishment of ions around the cathode and enables greater currentdensities to be effectively employed. As a result, the electrolyticprocess is speeded and the electrolytic action is more uniform. Moreadherent and bright platings which may be thicker than conventional andwhich are obtained in shorter periods of time are illustrative of theimproved electrolytic action achieved.

Example I Nickel sulfate (NiSO .6H O) 50.6 oz./gal. Nickel chloride(NiCl .6H O) 7.96 oz./ gal. Boric acid (H BO 6.5 z./gal. Wetting agent0.5% by volume.

This solution contained the equivalent to 12.85 02/ gal. of nickel(Ni++). and 2.38 oz./ gal. of chloride (Cl).

The bath was adjusted to a pH of 3.3 (electrometric) and purified bypotassium permanganate and activated carbon to remove organic impuritiesfrom the bath. This bath was then used to plate panels of polished highcarbon steel in a 1000 ml. Hullcell. The panels were preliminarilydegreased with a volatile solvent such as ether, air dried, and storedin dilute sodium cyanide solution. Before plating the panels were rinsedin water, dilute hydrochloric acid, and then again with water.

With straight direct current of 3 amperes at 6 volts, for 10 minutes,and with a bath temperature of 140 F. and agitation, a maximum of platethickness of .001" was obtained. The deposit was ductile and possessed amatte finish; With higher voltages and amperages, the quality of theplating decreased.

With high-speed periodic reverse current electroplating of the inventionusing a pulse interval of 0.3 second (forward 0.2 second, reverse 0.1second) and an energy ratio of 4 forward to 1 reverse (the averageforward voltage times the average forward current times forward timeinterval equals 4 times the average reverse voltage times averagereverse current times reverse time interval), a current of 8.5 amperesat 14 volts, greatly improved results were achieved. The temperature ofthe bath was started at 140 F. and rose to 165 F. and agitation wasused- In ten minutes the maximum deposit was over .002 in thickness.Optimum thickness was between .0018 and .002", and a bright ductilefinish was attained. This finish was good enough for chromium platingwithout bufling.

In the above example and the following examples, all parts are by weightunless otherwise specified.

Example II The following is an example of the application of theinvent-ion to rhodium plating, using as the plating bath 7.5 g./ gal. ofrhodium metal dissolved in 2 A 11. oz./gal. of sulfuric acid:

Anodes Platinum.

Temperature F.

Current density amps/sq. it, forward and reverse.

F o r w a r d time/reverse time 4:1. Pulse interval 0.3 sec. Voltage 3volts forward, .1 volt This deposited 0.2 mil bright rhodium plate overbright nickel in 2.5 rnins.

Example 111 This is an example of the application of the invention toplating nickel-tin alloy:

Plating solution:

Stannous chloride 5.8 oz./ga1. Nickel chloride 40.0 oz./gal. Sodiumfluoride 3.75 oz./gal. Ammonium bifiuoride 4.67 oz./gal. Anodes 1 tin:2nickel. Temperature F. Forward time/reverse time 4:1. Pulse interval 0.3sec. Curent density 200 amps./sq. ft. forward and reverse. Voltage 14volts.

This deposited 1 mil bright alloy plate in 5 min.

In each of Example IIll, no off period was used. The off period is notnecessary in all plating methods but is particularly applicable to somesolutions. Where there is no 01f period, the curve of Fig. 2, of course,would show no off period. In such a method, the tubes 15 and 13 aresuccessively energized by the controller 31, the tube 26 not beingutilized.

By way of example, the various values of the essential components shownin Fig. 1 may be as follows:

Component:

15, 18 06A. .26 CSB. r 17, 20 0-60 ohms, 500 w., plus a fixed resistorof 10 7 ohms, 500 w. 24 40 mfd. 28 10 mfd. 27 4 mfd. 29 5.0 ohms, 500 w.10 Generator-40 v., 40 a.,.

2 pole battery charging generator, rewound 2 coils/pole, 4. ohm/coil.

-The controller 31 is a conventional controller well known in the priorart and forms no part of the present invention.

The method of the invention may be utilized, for example, in platingnickel-tin alloy from a nickelous chloride, stannous chloride, sodiumand ammonium fluoride bath; plating copper from a cyanide bath; platingnickel from nickel sulfate baths; and plating copper from copperfiuoborate baths. Acid tin baths may also be used.

The ratio of forward time to reverse time and off period, if any, isvariable depending upon the metal being plated, the base metal, and thedegree of leveling required.

Generally, the current density which may be utilized in practicing theinvention ranges from 2-10 times that of conventional practice. Forexample, there may be used in nickel plating, 100-800 amps. per squarefoot; in nickel-tin alloy, 800 amps. per square foot; or in rhodium, 100amps. per square foot.

We claim:

1. Apparatus .for providing difierently directed unidirectional pulsesof electrical current with a rapid reversal of current directioncomprising, a D.C. generator having a pair of commutating interpoles andtwo oppositely wound field coils, the first of said field coils beingconnected on the one hand to the anode of a first arctype gas valvehaving an anode, a grid and a cathode, and on the other hand through aresistor to the positive terminal of a source of direct electricalcurrent, the second of said field coils being connected on the one handto the anode of a second arc-type gas valve having an anode, a grid anda cathode, and on the other hand through a second resistor to saidpositive terminal, said anodes being connected together through acapacitor so that the firing of one of said valves will extinguish theother of said valves, said cathodes being connected to the negativeterminal of said source of direct electrical current, and controllingmeans connected with said grids for supplying said grids with triggerpulses in timed sequence.

2. Apparatus as recited in claim 1 in which said resistors areadjustable. V v

3. Apparatus for providing differently directed unidirectional pulses ofelectrical current with a rapid reversal of current directioncomprising, a DC. generator having a pair of commutating interpoles andtwo oppositely wound field coils, the first of said field coils beingconnected on the one hand to the anode of a first arc-type gas valvehaving an anode, a grid and a cathode, and on the other hand through afirst resistor to the positive terminal of a source of direct electricalcurrent, the second of said field coils being connected on the one handto the anode of a second arc-type gas valve having an anode, a grid anda cathode, and on the other hand through a second resistor to saidpositive terminal, a third arc-type gas valve having an anode, a gridand a cathode, said third valve having its anode connected through athird resistor to said positive terminal, said anodes being connectedtogether through capacitors so that the firing of any one of said valvesWill extinguish the other of said valves, said cathodes being connectedto the negative terminal of said source of direct electrical current,and controlling means connected with said grids for supplying said gridswith trigger pulses in timed sequence.

4. Apparatus as recited in claim 3 in which said first and secondresistors are adjustable.

5. Apparatus for conducting an electrolytic process using difierentlydirected unidirectional pulses of electrical current with arapid'reversal of current direction comprising, a DC. generator having apair of commutating interpoles and two oppositely wound field coils,each of said interpoles being connected to an electrode, the first ofsaid field coils being connected on the one hand to the anode of a firstarc-type gas valve having an anode,

a grid and a cathode, and on the other hand through a resistor to thepositive terminal of a source of direct electrical current, the secondof said field coils being connected on the one hand to the anode of asecond arctype gas valve having an anode, a grid and a cathode, and onthe other hand through a second resistor to said positive terminal, saidanodes being connected together through a capacitor so that the firingof one of said valves will extinguish the other of said valves, saidcathodes being connected to the negative terminal of said source ofdirect electrical current, and controlling means connected with saidgrids for supplying said grids with trigger pulses in timed sequence.

6. Apparatus as recited in claim 5 in which said resistors areadjustable.

7. Apparatus for conducting an electrolytic process using differentlydirected unidirectional pulses of electrical current with a rapidreversal of current direction comprising, a DC. generator having a pairof commutating interpoles and two oppositely wound field coils, each ofsaid interpoles being connected to an electrode, the first of said fieldcoils being connected on the one hand to the anode of a first arc-typegas valve having an anode, a grid and a cathode, and on the other handthrough a first resistor to the positive terminal of a source of directelectrical current, the second of said field coils being connected onthe one hand to the anode of a second arctype gas valve having an anode,a grid and a cathode, and on the other hand through a second resistor tosaid positive terminal, a third arc-type gas valve having an anode, agrid and a cathode, said third valve having its anode connected througha third resistor to said positive terminal, said anodes being connectedtogether through capacitors so that the firing of any one of said valvesWill extinguish the other of said valves, said cathodes being connectedto the negative terminal of said source of direct electrical current,and controlling means connected with said grids for supplying said gridswith trigger pulses in timed sequence.

8. Apparatus as recited in claim 7 in which said first and secondresistors are adjustable.

9. Electroplating apparatus comprising, a DC generator having a pair ofcommutating interpoles and two oppositely wound field coils, each ofsaid interpoles being connected to an electrode, the first of said fieldcoils being connected on the one hand to the anode of a first arc-typegas valve having an anode, a grid and a cathode, and on the other handthrough a resistor to the posi tive terminal of a source of directelectrical current, the second of said field coils being connected onthe one hand to the anode of a second arc-type gas valve having ananode, a grid and a cathode, and on the other hand through a secondresistor to said positive terminal, said anodes being connected togetherthrough a capacitor so that the firing of one of said valves willextinguish the other of said valves, said cathodes being connected tothe negative terminal of said source of direct electrical current, andcontrolling means connected with said grids for supplying said gridswith trigger pulses in timed sequence.

10. Electroplating apparatus comprising, a DC. generator having a pairof commutating interpoles and two oppositely wound field coils, each ofsaid interpoles being connected to an electrode, the first of said fieldcoils being connected on the one hand to the anode of a first arc-typegas valve having an anode, a grid and a cathode, and on the other handthrough a first resistor to the positive terminal of a source of directelectrical current, the second of said field coils being connected onthe one hand to the anode of a second arc-type gas valve having ananode, a grid and a cathode, and on the other hand through a secondresistor to said positive terminal, a third arc-type gas valve having ananode, a grid and a cathode, said third valve having its anode connectedthrough a third resistor to said positive terminal, said anodes beingconnected together through capacitors so that the firing of any one ofsaid valves will extinguish the other of said valves, said cathodesbeing connected to the negative terminal of said source of directelectrical current, and controlling means connected with said grids forsupplying said grids with trigger pulses in timed sequence.

11. Apparatus for providing differently directed unidirectional pulsesof electrical current with a rapid reversal of current directioncomprising, a DC. generator having a pair of commutating interpoles andtwo oppositely wound field coils, the first of said field coils beingcon nected on the one hand to the anode of a first ,arctype gas valvehaving an anode, a grid and a cathode, and on the other hand to thepositive terminal of a source of direct electrical current, the secondof said field coils being connected on the one hand to the anode of asecond arc-type gas valve having an anode, a grid and a cathode, and onthe other hand to said positive terminal, said anodes being connectedtogether through a capacitor so that the firing of one of said valveswill extinguish the other of said valves, said cathodes being connectedto the negative terminal of said source of direct electrical current,and controlling means connected with said grids for supplying said gridswith trigger pulses in timed sequence.

12. Apparatus as recited in claim 11 wherein each field coil circuitincludes a variable resistor.

13. Apparatus for providing difierently directed unidirectional pulsesof electrical current with a rapid reversal of current directioncomprising, a DC. generator having a pair of commutating interpoles andtwo oppositely wound field coils, the first of said field coils beingconnected on the one hand to the anode of a first arc-type gas valvehaving an anode, a grid and a cathode, and on the other hand to thepositive terminal of a source of direct electrical current, the secondof said field coils being connected on the one hand to the anode of asecond arc-type gas valve having an anode, a grid and a cathode, and onthe other hand to said positive terminal, a third arc-type gas valvehaving an anode, a grid and a cathode, said third valve having its anodeconnected to said positive terminal, said anodes being connectedtogether through capacitors so that the firing of any one of said valveswill extinguish the other of said valves, said cathodes being connectedto the negative terminal of said source of direct electrical current,and controlling means connected with said grids for supplying said gridswith trigger pulses in timed sequence.

14. Apparatus as recited in claim 13 wherein each field coil circuitincludes a variable resistor.

15. Apparatus for providing difierently directed unidirectional pulsesof electrical current With a rapid reversal of current directioncomprising, a DC. generator having a pair of output terminals, fieldcoil means, a first electronic valve for directing current through saidfield coil means in one direction, a second electronic valve fordirecting current through said field coil means in the oppositedirection, and means to alternately actuate said valves to alternatelyexcite said field coil means with differently directed unidirectionalpulses.

16. Apparatus for providing diiferently directed uni: directional pulsesof electrical current With a rapid reversal of current directioncomprising, a DC. generator having a pair of output terminals, a first.field coil and a second oppositely wound field coil, a first electronicvalve for directing current through said first field coil, a secondelectronic valve for directing current through said second field coil,and means to alternately actuate said valves to alternately excite thefield coils with difierently directed unidirectional pulses.

17. Apparatus for providing differently directed unidirectional pulsesof electrical current with a rapid reversal of current directioncomprising, a DC. generator having a pair of output terminals, fieldcoil means, a first arc-type valve for directing current through saidfield coil means in one direction, a second arc-type valve for directingcurrent through said field coil means in the opposite direction, andcontrol means to alternately fire said valves in timed sequence toalternately excite said field coil means with differently directedunidirectional pulses.

18. Apparatus for providing differently directed unidirectional pulsesof electrical current with a rapid reversal of current directioncomprising, a DC. generator having a pair of output terminals, a firstfield coil, a second oppositely wound field coil, a first arc-type valvefor directing current through said field coils, a second arctype valvefor directing current through said second field coil, and control meansto alternately fire said valves in timed sequence to alternately excitethe field coils with dififerently directed unidirectional pulses.

19. Apparatus as recited in claim 18 includingmeans interconnecting saidvalves so that firing of one valve automatically extinguishes the othervalve.

20. Apparatus as recited in claim 18 including a third arc-type valvefor directing current through a load other than said field coils, meansinterconnecting all of said valves so that the firing of one of saidvalves automatically extinguishes the other valves, the firing of saidthird valve preventing excitation of the field coils of said D.C.generator.

, 21. Apparatus for providing differently directed unidirectional pulsesof electrical current with a rapid reversal of current directioncomprising, a DC. generator having a pair of output terminals,oppositely wound field coils, and means to alternately excite said coilswith unidirectional pulses of electrical current to reverse the field ofthe generator.

References Cited in the file of this patent UNITED STATES PATENTS2,451,341 Jernstedt Oct. 12, 1948 2,508,727 Shottenfeld et a1 May 23,1950 2,565,540 Williams Aug. 28, 1951 2,575,712 Jernstedt Nov. 20, 19512,634,393 Wu et a1. Apr. 7, 1953 2,678,909 Jernstedt et al May 18, 19542,696,582 Willard Dec. 7, 1954

